| Cables are widely used in power transmission and signal communication because of their safety,reliability,concealment,durability,and low environmental interference.With the increase in the number of cables used and their service life,the number of cable failures has gradually increased.Once the cable has a permanent failure,it will seriously affect the reliable operation of the power system and cause huge losses.Before a permanent failure occurs,it is of great significance to diagnose and warn the local defects of the cable as early as possible.The frequency domain reflection method based on the reflection coefficient spectrum of the head end is an emerging cable local defect location method.Aiming at the shortcomings of the current frequency domain reflection detection methods,a portable cable fault location measurement system is designed in this paper.The work content is as follows:(1)Starting from the transmission line theory,a cable distribution parameter model under the effect of frequency variation is established,the influence of local defects on the reflection coefficient spectrum of the cable head end is analyzed,and the mathematical expression for the localization of cable defects based on the frequency domain reflection method is derived.the effectiveness of the algorithm is demonstrated theoretically.(2)The numerical simulation model of cable local defect location is build based on the frequency domain reflection method.The positioning effect under different cable lengths,different cable types and different defect levels is analyzed,and the effectiveness of the frequency domain reflection algorithm from the simulation aspect is verified.The factors affecting the localization of cable defects are analyzed.(3)With the direct digital frequency synthesizer(DDS)as the core,the cable fault measurement system is designed and the hardware selection and circuit design of each module is completed.It includes modules such as signal generation circuit,separation circuit,detection circuit,processing circuit,storage circuit,and display circuit.Based on LABVIEW,the software for localized cable defect location analysis is developed.(4)a cable experiment platform to artificially create three different types of defects is built: local damage,local extrusion and local thermal aging.The local cable defects are located through the measurement system and vector network analyzer designed in this study,and the final measurement errors are measured.Contrast to verify the effectiveness of the measurement system.The experimental results show that the positioning error of the measurement system designed in this study is very close to that of the network analyzer,which can diagnose and warn the early local defect faults of the cable.It has good local defect localization capabilities and is comparable to the mature vector network analyzer.In comparison,the measurement system has better portability and reliability.It has certain practical engineering application value. |
